1. Field of the Invention
This invention relates to keyboard musical instruments and more particularly to a keyboard controlled just intonation computer which automatically corrects the larger tuning errors of the equal tempered scale as each interval or chord is played.
2. Description of the Prior Art
The theoretical basis for all prior art systems of just intonation for keyboard instruments is the assumption that all the harmonic resources required for most types of music can be derived from just scales of fixed pitch, one for each chosen tonality. As all prior art systems were scale determined they could not be fully automatic because scale selection requires additional mental and manual effort on the part of the player of the instrument. There were two approaches to the problem of scale selection.
One method was to have all the required notes playable by means of separate keys on a complex keyboard constructed in the form of a matrix so that harmonically related notes would lie within easily fingered rows of keys. Greater versatility with this approach could be achieved only at the expense of greater complexity of the keyboard. Typical of many such keyboard designs is the one disclosed in U.S. Pat. No. 2,232,600 to Arthur Fickensher.
The other method made it possible to simplify the keyboards or to retain the conventional keyboard by providing tonality stops which would cause the entire instrument to be retuned to any one of several just scales, one for each chosen tonality. For each modulation into a new key or for each new transposed chord, another tonality stop would have to be turned on. Typical of the tonality stop systems are U.S. Pat. No. 2,293,499 to Sidney T. Fisher and U.S. Pat. No. 2,525,524 to A. J. Chase.
The disadvantages of fixed scale systems will be evident from the following description: It is well known that the just scale C D E.sub.1 F G A.sub.1 B.sub.1 C which is generated by the perfectly tuned chords F A.sub.1 C, C E.sub.1 G and G B.sub.1 D, contains the imperfect minor chord D F A.sub.1 in which the note D is a comma too sharp relative to the note A.sub.1. On a fixed scale basis, a perfectly tuned chord D.sub.1 F A.sub.1 can be had only as the submediant triad in the key of F Major or as the mediant triad in the key of B Flat Major, by momentarily turning on either of these tonality stops. A further disadvantage of just intonation on a fixed scale basis is that the same mis-tuned triad D F A.sub.1 which would also be contained in the dominant ninth chord G B.sub.1 D F A.sub.1, renders that chord even more dissonant than the same chord in equal temperament. A correctly tuned chord G B.sub.1 D F.sub.2 A is available only by temporarily turning on the tonality stop for the key of G Major, if this scale has an additional note F.sub.2 about two commas lower than the normal note F. Therefore, the use of at least three tonality stops would be required to render in just intonation even the simplest music based upon the seven notes of the diatonic scale. In order to play music of greater harmonic complexity, in which chords are used for coloration of the melodic line as well as for definition of tonality, too much attention to tonality stops would be required and such music would be difficult, if not impossible, to play upon a multidigital keyboard. A useful description of typical present day organs may be found in a book entitled "Organ Builder's Guide" 1976, 3rd Edition by Roy L. DeVault and published by Devtronix Organ Products, 5872 Amapola Drive, San Jose, Calif. 95129.